In North America and elsewhere, it is common that large numbers of homes subscribe to a CATV to receive by coaxial cable a number of commercial and public television signals. Each signal consists of television video and audio, comprised of continuous audio and 30 (or 25) video frames per second. Each signal is transmitted down the coaxial cable by the CATV system to the subscriber's home television set over a discrete band of frequency known as a "channel". The subscriber tunes his television to the channel desired and receives the composite television signal.
It is not uncommon that a CATV have upwards of 50,000 subscribers. On such a large CATV, there is generally a central "hub" which acts as a control centre to receive the various signals, whether "broadcast" or satellite delivered, or locally generated by CATV operators or third parties. These signals are put on a trunk coaxial cable. Signal losses occur along the CATV coaxial cables and it is thus common that amplifiers, known in the trade as bridger amplifiers, be located at strategic locations, or nodes. Typically, therefore, a CATV system comprises a plurality of antennas adapted to receive signals from a plurality of broadcast stations or from satellite transponders. Amplifiers and the like located at a central hub amplify these signals and transmit each of them as a unique channel of frequencies onto one or more trunk coaxial cables. Along the trunk coaxial cable are a plurality of nodes. At each node a bridger amplifier amplifies the signals from the trunk and conveys the amplified signals onto one of a plurality of secondary distribution coaxial cables. Each secondary distribution cable has a plurality of "taps", each of which has a plurality of "drop" coaxial cables, one to each subscriber. Generally, any secondary distribution cable will service approximately 200 subscribers and there are normally between 50 and 100 taps so that each tap will service 2 to 4 drops.
Other systems have been developed to interactively distribute information to subscribers' televisions at their request. In order to be viable, such systems must:
1. service a large number of subscribers simultaneously; PA1 2. deliver high quality video images within a short response time; PA1 3. operate without requiring new hardware in the subscriber's home; and PA1 4. operate within the constraints of the number of television channels available on a typical CATV. Most CATV's have a maximum of approximately 15 "empty" channels. PA1 (A) a cable hub for receiving, generating and amplifying a plurality of television signals that are broadcast over predetermined frequency channels; PA1 (B) a trunk cable with one end connected to the cable hub to receive and transmit said signals to; PA1 (C) a plurality of nodes along said cable, each node adapted to convey said signals to; PA1 (D) a bridger amplifier connected to the trunk cable at each node and adapted to amplify and to transmit said signals onto; PA1 (E) a distribution cable for transmitting said amplified signals through; PA1 (F) a tap to a drop cable to a subscriber's home that is adapted for connection to a subscriber's television receiver; PA1 (G) a central control unit (CCU), located at the cable hub, comprising; PA1 (H) a node frame store, located at a node, to receive video frames and accompanying audio from the trunk cable and to transmit both onto the distribution cable; the node frame store including
No interactive system to date has succeeded in meeting all of the above requirements. Typically, the number of simultaneous users has been limited to a very small number. To send a live video image, one television channel is required for each subscriber; therefore, only approximately 15 subscribers could be serviced at one time. Or, in order to increase the number of simultaneous users, only computer graphics have been delivered, sacrificing picture quality and speed of delivery. The invention described in this application meets all four of the above-mentioned requirements. In addition, the invention delivers accompanying audio messages along with the video images, for a complete presentation.